Osteoporosis is a disease characterized by a decrease in bone mass which leads to a spontaneous bone fracture or fractures occurring due to an impact that under normal conditions would not produce a bone fracture. The goal for treating osteoporosis is to build bone strength to a level sufficient to withstand normal loading conditions without failure. A significant determinant of bone strength is bone mass. Bone mass is determined by the balance between the activity of osteoclast, which destroy bone, and osteoblast, which build bone. During homeostasis, in which bone mass is maintained at a constant level, the activity of the osteoclast and osteoblast are equal. Around the age of thirty, peak bone mass is typically achieved. At this stage the activity of osteoblasts begin to lag behind the activity of osteoclasts. This results in a loss of bone. The health impact of osteoporosis includes loss of the quality of life as osteoporotic bone fractures usually occur in the elderly who have a diminished healing capacity.
One method of treatment is to stimulate osteoblast to form new bone. It is well known in biology that mature, fully differentiated cells do not divide to create new cells. Therefore, to increase the number of bone producing, fully differentiated bone cells it is necessary to first increase the number of pre-osteoblast cells and then induce their maturation into fully differentiated bone cells to reverse the effects of osteoporosis. Furthermore, since new bone cell growth is also needed to heal non-osteoporotic bone fractures and to fuse vertebrae, the stimulation of osteoblasts to form new bone is also useful for treating other fractures and for performing spinal fusion.